Phase relations in the system PbS-SnS-SnS 2 -Sb 2 S 3 were studied using the evacuated glass-capsule technique. Sulfide phases found at 500 degrees C, in addition to the end members, are PbS . SnS (teallite), SnS . SnS 2 (ottemannite), 3SnS . Sb 2 S 3 , PbS . Sb 2 S 3 (zinkenite), 6PbS . 5Sb 2 S 3 (robinsonite), 5PbS . 2Sb 2 S 3 (boulangerite), and three new phases, designated as I, II, and III.Phase I has a composition of PbS . SnS 2 and can take 2 mole%SnS 2 in excess along the binary join PbS-SnS 2 . It is isostructural with SnS . SnS 2 with a 0 = 8.74A, b 0 = 14.03A, and c 0 = 3.76A and forms a complete solid solution with SnS . SnS 2 in the system PbS-SnS-SnS 2 . Phase I melts congruently at 730 degrees + or - 5 degrees C.Phases II and III have compositions in the ranges limited, respectively, by 62.5 to 74 mole%SnS, 10.0 to 15.5 mole%SnS 2 , 13.0 to 25.0 mole%Sb 2 S 3 , and 57.0 to 64.0 mole%-PbS, 18.0 to 28.0 mole%SnS 2 , 13.5 to 21.0 mole%Sb 2 S 3 . Phase II forms equilibrium assemblages with all phases in the system SnS-SnS 2 -Sb 2 S 3 , whereas phase assemblages containing Phase III are limited in the PbS-rich portion of the system PbS-SnS 2 -Sb 2 S 3 . Both phases melt incongruently; Phase II (Sn (sub 0.70) (super +2) Sn (sub 0.15) (super +4) Sb (sub 0.30) S (sub 1.45) ) at 627 degrees + or - 5 degrees C to SnS . SnS 2 and liquid, and Phase III (Pb (sub 0.60) Sn (sub 0.23) (super +4) Sb (sub 0.34) S (sub 1.57) ) at 617 degrees + or - 5 degrees C to Phase I and liquid.In the system PbS-SnS-Sb 2 S 3 , liquid is the predominant phase and forms equilibrium assemblages with Sb 2 S 3 , PbS . Sb 2 S 3 , and 3SnS . Sb 2 S 3 at 500 degrees C. Neither solid solution nor ternary phases were found.The system PbS-SnS-SnS 2 -Sb 2 S 3 is characterized by the formation of a complete series of solid solution between Phase II and Phase III.Neither cylindrite nor franckeite was found to exist in the system PbS-SnS-SnS 2 -Sb 2 S 3 . Both minerals, however, were synthesized from compositions containing iron.

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